Zirconia powder

Abstract

The present invention provides a zirconia powder exhibiting excellent sinterability at low temperatures, a method for producing the same, and at least one of the following: a method for producing a zirconia sintered body obtained from the zirconia powder, a method for producing an electrolyte, a method for producing a solid oxide fuel cell, and a method for producing a solid oxide electrolytic cell. [Solution] Zirconia powder containing chlorine and stabilizing elements, wherein the chlorine content is 0.001% by mass or more and 0.300% by mass or less, the difference between the BET specific surface area after heat treatment at 1000°C for 2 hours in an air atmosphere and the BET specific surface area before heat treatment is 3.0 or more and 30.0 or less, and the zirconia content is 75% by mass or more.

Description

[Technical Field]

[0001] This disclosure relates to zirconia powder. [Background technology]

[0002] Stabilized zirconia is used in a wide range of applications, including grinding, optical, decorative, dental, and battery materials. For example, Patent Document 1 reports cubic scandia-stabilized zirconia containing scandia (Sc2O3) and ceria (CeO2) as a stabilized zirconia. In Patent Document 1, zirconia powder is obtained from chlorides such as zirconium oxychloride, scandium chloride, and cerium chloride as raw materials, and this is mixed with a solvent to form a slurry. A stabilized zirconia film is then produced by coating, drying, and firing the slurry to sinter the zirconia powder. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2016-108165 [Overview of the project] [Problems that the invention aims to solve]

[0004] The zirconia powder used in the production of stabilized zirconia films described in Patent Document 1 required a high firing temperature of 1420°C for sufficient sintering. As the firing temperature increases, the energy required also increases. Furthermore, carbon dioxide emissions increase along with the increase in energy. From the perspective of reducing environmental impact, there is a need for zirconia powder that can be sintered at lower temperatures by improving the energy efficiency during firing.

[0005] The present disclosure aims to provide a zirconia powder that exhibits excellent sinterability at low temperatures and a method for producing the same, as well as a method for producing a zirconia sintered body obtained from the zirconia powder, a method for producing an electrolyte, a method for producing a solid oxide fuel cell, and a method for producing a solid oxide electrolytic cell. [Means for solving the problem]

[0006] In this disclosure, we investigated factors that inhibit sintering in zirconia powder used in the production of stabilized zirconia. As a result, we found that chlorine inhibits the diffusion of zirconium and stabilizing elements in the sintering process of zirconia powder containing stabilizing elements, and we found that stabilized zirconia can be obtained at a lower firing temperature by reducing the amount of chlorine in the zirconia powder.

[0007] In other words, the present invention is as described in the claims, and the gist of this disclosure is as follows: [1] Zirconia powder containing chlorine and stabilizing elements, wherein the chlorine content is 0.001% by mass or more and 0.300% by mass or less, the difference between the BET specific surface area after heat treatment at 1000°C for 2 hours in an air atmosphere and the BET specific surface area before heat treatment is 3.0 or more and 30.0 or less, and the zirconia content is 75% by mass or more. [2] The zirconia powder according to [1] above, wherein the stabilizing element comprises at least one selected from scandium, yttrium, ytterbium, cerium, and samarium. [3] The zirconia powder according to [2] above, wherein the stabilizing element comprises scandium and at least one selected from yttrium, ytterbium, cerium, and samarium. [4] The stabilizing element includes scandium, The scandium content is between 5.0 mol% and 11.0 mol%. The zirconia powder described in [2] or [3] above. [5] The BET specific surface area before the heat treatment was 11.0 m². 2 / g or more 30.0m2 The value is less than or equal to / g, and the BET specific surface area after the heat treatment is 3.0 m². 2 / g or more 10.0m 2 Zirconia powder according to any one of the above [1] to [4], wherein the amount is less than or equal to / g. [6] The zirconia powder according to any one of the above [1] to [5], wherein the additive element other than the stabilizing element is at least one selected from aluminum, silicon, and germanium. [7] A method for producing zirconia powder according to any one of the above [1] to [6], comprising: a first calcination step of mixing a zirconia sol obtained using zirconium chloride with a stabilizing element source and heat-treating it at a holding temperature of 600°C to 850°C to obtain a powder precursor; a washing step of washing the powder precursor with an aqueous ammonia solution; and a second calcination step of heat-treating the washed powder precursor at a holding temperature of over 850°C and 950°C to obtain zirconia powder. [8] A method for producing a zirconia sintered body using the powder described in any one of the above items [1] to [6]. [9] A method for producing an electrolyte using the powder described in any one of the above items [1] to [6].

[10] A method for manufacturing a solid oxide fuel cell, comprising the step of firing a laminated precursor having a structure in which an electrolyte precursor layer is sandwiched between a fuel electrode precursor layer and an air electrode precursor layer, wherein the electrolyte precursor layer is an electrolyte precursor sheet containing the powder described in any one of the above [1] to [6] or a fired product thereof.

[11] A method for manufacturing a solid oxide electrolytic cell, comprising the step of firing a laminated precursor having a structure in which an electrolyte precursor layer is sandwiched between a fuel electrode precursor layer and an air electrode precursor layer, wherein the electrolyte precursor layer is an electrolyte precursor sheet containing the powder described in any one of the above [1] to [6] or a fired product thereof. [Effects of the Invention]

[0008] This disclosure provides a zirconia powder with excellent low-temperature sinterability and a method for producing the same, as well as a method for producing a zirconia sintered body obtained from the zirconia powder, a method for producing an electrolyte, a method for producing a solid oxide fuel cell, and a method for producing a solid oxide electrolytic cell. [Brief explanation of the drawing]

[0009] [Figure 1] Schematic diagram showing the electrolyte-supported cell of this embodiment. [Figure 2] A schematic diagram showing the fuel electrode-supported cell of this embodiment. [Figure 3] Schematic diagram showing the metal-supported cell of this embodiment [Modes for carrying out the invention]

[0010] The present disclosure will be described below with reference to an example of an embodiment. Furthermore, the present disclosure includes any combination of the configurations and parameters disclosed herein, as well as any combination of the upper and lower limits of the values ​​disclosed herein. The terms used in this embodiment are as follows.

[0011] "Powder" refers to a composition that is an aggregate of powder particles and also possesses fluidity. "Zirconia powder" refers to a powder whose main component is zirconia, and is essentially a powder made of zirconia.

[0012] The "main component" is the component that constitutes the main phase (matrix, base material, parent phase) in the composition of the composition, and preferably has a mass percentage of 75% by mass or more, 85% by mass or more, 90% by mass or more, 95% by mass or more, 98% by mass or more, or 99% by mass or more, and is a component that is 100% by mass or less or less by mass.

[0013] The chlorine content [mass%] (hereinafter also referred to as "chlorine content") can be determined by measuring the zirconia powder to be measured using an X-ray fluorescence analyzer, based on a calibration curve prepared in advance using reference substances (multiple zirconia powders with different chlorine concentrations; for example, four types of zirconia powders with chlorine concentrations ranging from 0% by mass to 1.0% by mass). The calibration curve can be prepared as follows: Prepare multiple reference substances with different chlorine concentrations, add 2 ml of silver standard solution (Ag concentration 1 g / L), 3 ml of nitric acid, and 15 ml of hydrofluoric acid to 0.2 to 0.5 g of each reference substance, stir, and heat at 170°C for 16 hours to dissolve the reference substance. Then, let the solution stand in a cool, dark place for 2 hours. This causes chloride ions from the reference substance to react with silver ions from the silver standard solution, resulting in the precipitation of silver chloride (AgCl). The amount of precipitated silver chloride is calculated by filtering out the silver chloride and quantifying the silver ions in the filtrate using an ICP emission spectrometer (e.g., Optima 5300 DV, Perkin Elmer). Specifically, the difference between the amount of Ag in the silver standard solution and the amount of Ag in the filtrate corresponds to the amount of Ag in the precipitated silver chloride, thus calculating the amount of silver chloride. Here, the amount of chlorine in the silver chloride corresponds to the amount of chlorine in the reference substance. From this calculation result, the chlorine concentration [mass%] of the reference substance is determined. On the other hand, the standard sample is pressure-molded into a pellet-shaped sample, and the sample is measured using an X-ray fluorescence analyzer (e.g., ZSM PrimusII A-126, Rigaku Corporation) to obtain the X-ray fluorescence intensity. The chlorine concentration obtained in this way is plotted on the x-axis and the X-ray fluorescence intensity on the y-axis, and each reference substance is plotted. An approximate straight line created from each plot so that the correlation coefficient is 0.950 or higher can be used as the calibration curve.

[0014] "BET specific surface area" is the specific surface area [m²] measured by the BET multi-point method (5 points) using nitrogen as the adsorbent gas, in accordance with JIS R 1626-1996. 2 [ / g] is the BET specific surface area measured under the following conditions.

[0015] Adsorption medium: N2 Adsorption temperature: -196℃ Pretreatment conditions: Degassing treatment at 250°C for at least 1 hour in an air atmosphere. The BET specific surface area can be measured using a general specific surface area measuring device (for example, device name: Tristar II 3020, manufactured by Shimadzu Corporation). Note that "atmospheric atmosphere" refers to an atmosphere mainly composed of nitrogen and oxygen, specifically a nitrogen atmosphere with an oxygen concentration of 18-23% by volume, which may also contain moisture.

[0016] An "XRD pattern" is the XRD pattern of a composition obtained by powder X-ray diffraction (hereinafter also referred to as "XRD") measurement under the following conditions.

[0017] Radiation source: CuKα radiation (λ=0.15418nm) Measurement mode: Continuous scan Scan speed: 4° / min Step width: 0.02° Measurement range: 2θ = 26.0° ~ 33.0° Acceleration voltage / current: 40mA / 40kV Divergence vertical limiting slit: 10mm Divergence / Induction Slit: 1° Light-receiving slit: open Detector: Semiconductor detector (D / teX Ultra) Filter: Ni filter Goniometer radius: 185mm XRD measurements can be performed using a standard X-ray diffractometer (e.g., Ultima IV, manufactured by Rigaku Corporation).

[0018] An "XRD peak" is a peak with a peak top at 2θ detected in the XRD pattern obtained in the above-described XRD measurement. The XRD peak can be detected by profile fitting the XRD pattern after smoothing and background removal (hereinafter also referred to as the "processed XRD pattern") using a segmented pseudo-Voigt function. The analysis of the XRD pattern, including smoothing, background removal, and XRD peak detection, can be performed using an analysis program attached to the X-ray diffractometer (for example, the integrated powder X-ray analysis software PDXL Ver.2.2, manufactured by RIGAKU Corporation) under the following conditions. In this embodiment, what is detected in this way is referred to as the XRD peak. Note that the XRD pattern and processed XRD pattern may contain minute peaks (so-called noise) that are not detected in the fitting. In this embodiment, "not having an XRD peak" means that the XRD peak is not detected in the above-described XRD measurement.

[0019] Scherrer constant: 1.000 Smoothing method: Smoothing using β-spline, γ-threshold = 1.50 Background removal method: A straight line connecting the endpoints Kα2 ray removal method: intensity ratio=0.497 Peak search method: Peak top method, alpha cut value = 3.00 Profiling fitting method: Split pseudo-Voigt function The XRD peaks corresponding to each crystal plane of zirconia are XRD peaks with peak tops at the following 2θ.

[0020] XRD peak corresponding to the monoclinic (111) plane: 2θ = 31.5 ± 0.5° XRD peak corresponding to the monoclinic (-111) plane: 2θ = 28.0 ± 0.5° XRD peak corresponding to the tetragonal (101) plane: 2θ = 30.0 ± 0.5° XRD peak corresponding to the cubic (111) plane: 2θ = 30.0 ± 0.5° The XRD peak corresponding to the (101) plane of the tetragonal crystal and the XRD peak corresponding to the (111) plane of the cubic crystal are measured as one overlapping peak.

[0021] The "monoclinic ratio" is the ratio of the area intensity of the XRD peak of monoclinic zirconia to the total area intensity of the XRD peaks of tetragonal, cubic, and monoclinic zirconia in the XRD pattern obtained in the above XRD measurement, and is obtained from the following formula.

[0022] f m =[I m (111)+I m (-111)] / [I m (111)+I m (-111)+I t (101)+I c (111)]×100 In the above formula, f m is the monoclinic ratio, I t (101) is the area intensity of the (101) plane of the tetragonal crystal, I c (111) is the area intensity of the (111) plane of the cubic crystal, I m (111) is the area intensity of the (111) plane of the monoclinic crystal, I m (-111) is the area intensity of the (-111) plane of the monoclinic crystal, and I<00asmuch as possible, the area intensity of the XRD peak having a peak top at 2θ = 30.0 ± 0.5°.

[0023] The area intensity of each XRD peak can be obtained by using "PRO-FIT" in the calculation program and separating each XRD peak by the method described in H. Toraya, J. Appl. Crystallogr., 19, 440 - 447 (1986).

[0024] The "average crystallite size" is the crystallite size obtained from the XRD peak where the (101) plane of the tetragonal crystal and the (111) plane of the cubic crystal overlap (hereinafter also referred to as the "main XRD peak"), and is a value calculated from the following formula.

[0025] ​​​ D = κλ / βcosθ In the above equation, D is the average crystallite size (Å), κ is the Scherer constant (κ=1), λ is the wavelength of the measured X-ray (λ=0.15418 nm when CuKα is used as the source), β is the full width at half maximum (FWHM) of the main XRD peak (°), and θ is the Bragg angle of the main XRD peak. Note that β is the FWHM value of the main XRD peak obtained by profile fitting the XRD pattern after smoothing and background removal using a divided pseudo-Voigt function. Profile fitting can be performed using an analysis program attached to the X-ray diffractometer (for example, the integrated powder X-ray analysis software PDXL Ver.2.2, manufactured by RIGAKU Corporation).

[0026] "Average sol particle size" refers to the median diameter (D50) at which the particle size distribution and integrated particle size distribution curves intersect the 50% horizontal axis when zirconia sol is measured using a general dynamic light scattering particle size distribution analyzer (e.g., UPA-UT151, manufactured by Microtrac-Bell). As a pretreatment before measurement, the zirconia sol-containing solution is suspended in pure water and dispersed for 3 minutes using an ultrasonic homogenizer.

[0027] "Average particle size" refers to the particle size (median diameter) that corresponds to 50% of the volume of the cumulative volume particle size distribution curve of a powder obtained by volume particle size distribution measurement using laser diffraction with a general-purpose instrument (e.g., MT3300II, manufactured by Microtrac-Bell).

[0028] "Measured density" is calculated using the sample volume [cm³]. 3 The value [g / cm] can be obtained from the mass [g] of ]. 3 The mass should be the mass obtained by weighing the sample, and the sample volume should be the volume determined by the Archimedes method in accordance with JIS R 1634. Prior to measurement, the mass of the sintered body after drying should be measured, then the sintered body should be placed in water and boiled for 1 hour as a pretreatment.

[0029] [Zirconia powder] This embodiment is a zirconia powder (hereinafter also referred to as "the powder of this embodiment") that contains chlorine and a stabilizing element, wherein the chlorine content is 0.001% by mass or more and 0.30% by mass or less, and the difference between the BET specific surface area after heat treatment at 1000°C for 2 hours in an air atmosphere and the BET specific surface area before heat treatment is 3.0 or more and 30.0 or less.

[0030] The powder of this embodiment is a powder mainly composed of zirconia and containing stabilizing elements. The powder of this embodiment is composed of powder particles. The powder particles include primary particles, which are the smallest independent units of particles, and secondary particles, which are particles formed by the physical aggregation of primary particles.

[0031] The powder of this embodiment has a chlorine content of 0.001% by mass or more and 0.300% by mass or less. The upper limit of the chlorine content is preferably 0.250% by mass or less, 0.200% by mass or less, 0.150% by mass or less, 0.100% by mass or less, or 0.070% by mass or less, and the lower limit is preferably 0.010% by mass or more and 0.015% by mass or more. The chlorine content of the powder of this embodiment can be 0.001% by mass or more and 0.250% by mass or less, 0.001% by mass or more and 0.200% by mass or less, 0.001% by mass or more and 0.150% by mass or less, 0.010% by mass or more and 0.100% by mass or less, or 0.010% by mass or more and 0.070% by mass or less.

[0032] The powder of this embodiment exhibits excellent low-temperature sinterability due to its chlorine content being within the aforementioned range. Specifically, because the powder of this embodiment has a reduced chlorine content that inhibits the diffusion of zirconia and stabilizing elements during sintering, the stabilizing elements diffuse well even when fired at low temperatures (for example, between 1050°C and 1300°C), resulting in a dense sintered body.

[0033] The powder of this embodiment has a specific surface area difference (BET) of 3.0 to 30.0 after heat treatment at 1000°C for 2 hours in an air atmosphere compared to the BET specific surface area before heat treatment (this is the difference between the BET specific surface area before heat treatment and the BET specific surface area after heat treatment; hereinafter also referred to as the "specific surface area difference"). Preferably, the upper limit of the specific surface area difference is 28.0 or less, 26.0 or less, 24.0 or less, or 22.0 or less, and also preferably 6.0 or more, 9.0 or more, 10.0 or more, or 12.0 or more. Examples of specific surface area differences for the powder of this embodiment include 6.0 to 28.0, 9.0 to 26.0, 10.0 to 24.0, or 12.0 to 22.0. The above-mentioned specific surface area difference is considered to be one indicator of the state of presence of zirconia, stabilizing elements, and chlorine in the powder of this embodiment. The fact that the difference in specific surface area is within the range described above indicates that the stabilizing elements have diffused appropriately within the powder of this embodiment.

[0034] The powder of this embodiment has a BET specific surface area (hereinafter also referred to as "BET before heat treatment") of 11.0 m² before heat treatment at 1000°C for 2 hours in the aforementioned atmospheric environment. 2 / g or more, 14.0m 2 / g or more, 17.0m 2 / g or more, or 19.0m 2 It is preferable that the amount be 30.0m or more, and also 30.0m 2 / g or less, 27.0m 2 / g or less, 25.0m 2 / g or less, or 22.0m 2 It is preferable that the amount is less than or equal to / g. The pre-heat treatment BET of the powder in this embodiment is 11.0m 2 / g or more 30.0m 2 / g or less, 11.0m 2 / g or more 27.0m 2 / g or less, 11.0m 2 / g or more 25.0m 2 / g or less, 14.0m 2 / g or more 25.0m 2 / g or less, or 17.0m 2 / g or more 22.0m 2 One example is that it should be less than or equal to / g.

[0035] The powder of this embodiment has a BET specific surface area (hereinafter also referred to as "post-heat-treated BET") of 3.0 m² after heat treatment at 1000°C for 2 hours in an air atmosphere. 2 / g or more, 3.5m 2 / g or more, or 4.0m 2 It is preferable that it be 10.0 m or more, and also 10.0 m 2 / g or less, 9.0m 2 / g or less, or 8.0m 2 It is preferable that the amount is less than or equal to / g. The BET of the powder after heat treatment in this embodiment is 3.0m 2 / g or more 10.0m 2 / g or less, 3.5m 2 / g or more 9.0m 2 / g or less, or 4.0m 2 / g or more 8.0m 2 One example is that it should be less than or equal to / g.

[0036] The powder of this embodiment has a specific surface area difference of 6.0 to 28.0 and a BET before heat treatment of 11.0 m². 2 / g or more 30.0m 2 / g or less, and BET after heat treatment is 3.0m 2 / g or more 10.0m 2 Preferably, the density is less than or equal to / g, the specific surface area difference is between 9.0 and 26.0, and the BET before heat treatment is 11.0 m². 2 / g or more 27.0m 2 / g or less, and BET after heat treatment is 3.5m 2 / g or more 9.0m 2 It is more preferable that the amount is less than or equal to / g, the specific surface area difference is between 10.0 and 24.0, and the BET before heat treatment is 11.0 m². 2 / g or more 25.0m 2 / g or less, and BET after heat treatment is 4.0m 2 / g or more 8.0m 2 It is even more preferable that the amount is less than or equal to / g, the specific surface area difference is between 12.0 and 22.0, and the BET before heat treatment is 14.0 m². 2 / g or more 25.0m 2 / g or less, and BET after heat treatment is 4.0m 2 / g or more 8.0m 2 It is particularly preferable that the amount be less than or equal to / g.

[0037] The powder of this embodiment contains a stabilizing element. The stabilizing element is an element that has the function of stabilizing the crystalline phase of zirconia, and includes one or more selected from the group consisting of scandium (Sc), yttrium (Y), ytterbium (Yb), cerium (Ce), samarium (Sm), calcium (Ca), and magnesium (Mg), and also includes one or more selected from the group consisting of scandium, yttrium, ytterbium, cerium, and samarium, and further includes scandium. In addition, if the powder of this embodiment contains two or more stabilizing elements, it may include scandium and one or more selected from the group consisting of yttrium, ytterbium, cerium, and samarium. In addition, if the powder of this embodiment contains two or more stabilizing elements, it may also include scandium and one or more selected from the group consisting of yttrium, ytterbium, and cerium.

[0038] The content of stabilizing elements in the powder of this embodiment (hereinafter also referred to as "amount of stabilizing elements," and if the stabilizing element is scandium, also referred to as "amount of scandium") is preferably greater than 0 mol%, 0.1 mol% or more, 1.0 mol% or more, 2.0 mol% or more, 4.0 mol% or more, or 6.0 mol% or more, and also preferably 25.0 mol% or less, 20.0 mol% or less, 15.0 mol% or less, 13.0 mol% or less, 12.0 mol% or less, or 11.0 mol% or less. Examples of the amount of stabilizing elements in the powder of this embodiment include greater than 0 mol% and 25.0 mol% or less, 0.1 mol% or more and 20.0 mol% or less, 1.0 mol% or more and 15.0 mol% or less, 2.0 mol% or more and 13.0 mol% or less, 4.0 mol% or more and 12.0 mol% or less, or 6.0 mol% or more and 11.0 mol% or less.

[0039] In this embodiment, the amount of stabilizing elements is the ratio [mol%] of the stabilizing elements in oxide equivalent to the total amount of zirconia and the stabilizing elements in oxide equivalent. If the powder contains multiple stabilizing elements, the amount of stabilizing elements in oxide equivalent is the sum of each stabilizing element in oxide equivalent.

[0040] The powder of this embodiment exhibits particularly excellent sinterability at low temperatures, especially when it contains scandium as a stabilizing element, due to the chlorine content being within the range described above.

[0041] Conventionally, reducing the chlorine content of scandium-containing zirconia powder has been difficult for the following reasons. First, a widely used industrial method for producing scandium-containing zirconia powder involves using chlorides such as zirconium oxychloride and scandium chloride as raw materials, and then drying and calcining the resulting intermediate to obtain the powder (Patent Document 1). Here, calcination allows stabilizing elements to be dissolved and diffused into the zirconia, while chlorine derived from the raw materials is removed. Because scandium has an ionic radius close to that of zirconium, its diffusion in the zirconia powder during calcination proceeds at a lower temperature. Therefore, if the calcination temperature is too high, sintering proceeds too much. If sintering proceeds too much during calcination, the BET specific surface area of ​​the resulting zirconia powder becomes too small, which reduces contact between the zirconia powder particles when the zirconia powder is molded and sintered to produce a sintered body. As a result, densification during sintering is inhibited, and the resulting sintered body is prone to defects. Therefore, when manufacturing zirconia powder containing scandium, it is preferable to perform calcination at a low temperature (for example, 950°C or lower). On the other hand, chlorine derived from the chloride raw material was conventionally removed by calcination at high temperatures. Therefore, if the calcination temperature is low, chlorine remains in the zirconia powder. In contrast, the powder of this embodiment makes it possible to prevent excessive sintering while maintaining a chlorine content that does not affect sinterability.

[0042] Furthermore, the ionic radii of Zr, Sc, and Y in 8-coordinate systems are from Acta Crystallographica A32, 751-767 (1976), 4+ 0.84 Å, Sc 3+ 0.87 Å, Y 3+ This is 1.019 Å.

[0043] The powder of this embodiment may contain additive elements different from the stabilizing elements described above. The additive elements are elements that can impart coloration or other additional functions to zirconia, and include one or more selected from the group consisting of aluminum (Al), silicon (Si), germanium (Ge), lanthanide rare earth elements other than the stabilizing elements described above, and transition metal elements other than zirconium (Zr) and hafnium (Hf), and one or more selected from the group consisting of aluminum, silicon, and germanium. Lanthanide rare earth elements other than stabilizing elements include, for example, one or more selected from the group consisting of praseodymium (Pr), neodymium (Nd), europium (Eu), gadolinium (Gd), terbium (Tb), and erbium (Er). Furthermore, examples of transition metal elements other than zirconium and hafnium include one or more selected from the group consisting of manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), and silver (Ag), as well as one or more selected from the group consisting of iron, cobalt, nickel, neodymium, gadolinium, terbium, and erbium.

[0044] Furthermore, the powder of this embodiment may contain additive elements (hereinafter also referred to as "amount of additive elements," and if the additive element is aluminum, it may also be referred to as "aluminum amount") of 0% by mass or more, contain additive elements and have an amount greater than 0% by mass or 0.01% by mass or more, and also have an amount of 0.25% by mass or less or 0.1% by mass or less, and furthermore have an amount of 0% by mass or more or 0.25% by mass or less, or greater than 0% by mass or less or 0.1% by mass or less. In other forms of this embodiment, it is preferable that the powder of this embodiment substantially contains no additive elements (the amount of additive elements is 0% by mass), and examples include the amount of additive elements being 0.03% by mass or less, 0.01% by mass or less, or 0.005% by mass or less, and also have an amount of 0% by mass or more or 0.03% by mass or less, 0% by mass or more or 0.01% by mass or less, or 0% by mass or more or 0.005% by mass or less.

[0045] The amount of added elements is the mass ratio [mass%] of the added elements in oxide form to the total mass of zirconia and the added elements in oxide form. If the powder contains multiple added elements, the amount of added elements in oxide form is the sum of the amounts of each added element in oxide form.

[0046] In this embodiment, the oxide equivalents of each element are as follows: Zirconium is ZrO2, Scandium is Sc2O3, Yttrium is Y2O3, Ytterbium is Yb2O3, Cerium is CeO2, Samarium is Sm2O3, Calcium is CaO, Magnesium is MgO, Aluminum is Al2O3, Silicon is SiO2, Germanium is Ge2O3, Praseodymium is Pr2O3, Neodymium is Nd2O3, Europium is Eu2O3, Gadolinium is Gd2O3, and Terbium is Tb7O 11 The following are required: erbium is Er2O3, manganese is Mn3O4, iron is Fe2O3, cobalt is Co3O4, nickel is NiO, copper is CuO, molybdenum is Mo2O3, technetium is TcO2, ruthenium is Ru2O3, rhodium is Rh2O3, palladium is Pd2O3, and silver is AgO.

[0047] The powder of this embodiment is preferably free of impurities, but may contain impurities as long as it does not impair its intended effect. Specific examples of impurities include alkali metal elements, and at least one of sodium (Na) and potassium (K). On the other hand, the powder of this embodiment may also contain hafnia (HfO2), which is an unavoidable impurity of zirconia. The calculation of compositional values ​​in this embodiment can be performed by treating hafnia as zirconia.

[0048] The monoclinic content of the powder in this embodiment is preferably 15.0% or less, 10.0% or less, 5.0% or less, 1.0% or less, or 0.5% or less. The lower limit of the monoclinic content is 0% or more. By having the monoclinic content within the above range, the sintering temperature required for densification during sintering of the powder can be lowered, and coarse pores can be further reduced as densification progresses.

[0049] The average crystallite diameter of the powder in this embodiment is preferably 15 nm or more, or 20 nm or more, and preferably 40 nm or less, or 30 nm or less. The average crystallite diameter of the powder in this embodiment is 15 nm or more and 40 nm or less, or 20 nm or more and 30 nm or less.

[0050] The average particle size of the powder in this embodiment is preferably 0.50 μm or less, 0.40 μm or less, 0.35 μm or less, or 0.30 μm or less, and also preferably 0.05 μm or more, or 0.10 μm or more. The average particle size of the powder in this embodiment can be 0.05 μm or more and 0.50 μm or less, 0.05 μm or more and 0.40 μm or less, 0.05 μm or more and 0.35 μm or less, or 0.10 μm or more and 0.30 μm or less.

[0051] From the viewpoint of further improving moldability, the powder of this embodiment preferably has a volume particle size distribution in which particles of 0.25 μm or less (hereinafter also referred to as the "fine particle ratio") account for 10% or more, 20% or more, or 30% or more, and also preferably 90% or less, 80% or less, or 70% or less. The fine particle ratio of the powder of this embodiment can be 10% or more and 90% or less, 20% or more and 80% or less, or 30% or more and 70% or less.

[0052] In this embodiment, from the viewpoint of easily obtaining a dense sintered body even at lower sintering temperatures, it is preferable that the powder has a particle size peak with a peak top of 0.1 μm or more and 0.5 μm or less in its volume particle size distribution. Furthermore, it is preferable that the width of the particle size peak is 0.05 μm or more and 0.4 μm or less.

[0053] The powder of this embodiment can be used in known applications of zirconia powder, such as structural materials, decorative materials, optical materials, electronic equipment casings, high-temperature components (heat dissipation components, heat treatment containers, setters, furnace core tubes, temperature-measuring protective tubes, etc.), insulating components, light-emitting tubes, battery cell materials, or electrolytic cell materials. However, it is preferable to use it as a battery cell material or electrolytic cell material, and more preferably as a material for the electrolyte constituting a solid oxide fuel cell or solid oxide electrolytic cell (hereinafter also referred to as "SOFC / EC"). Examples of SOFC / ECs in which the powder of this embodiment is used include electrolyte-supported cells, fuel electrode-supported cells, and metal-supported cells. Cell stacks formed by stacking such cells can be used in fuel cells and water electrolysis devices.

[0054] [Method for producing zirconia powder] The manufacturing method for the powder of this embodiment is arbitrary as long as a zirconia powder satisfying the above-described configuration can be obtained. However, a preferred manufacturing method is a method for producing zirconia powder (hereinafter also referred to as "the manufacturing method of this embodiment") which includes: a first calcination step in which a zirconia sol obtained using zirconium chloride is mixed with a stabilizing element source and heat-treated at a holding temperature of 600°C to 850°C to obtain a powder precursor; a washing step in which the powder precursor is washed with an aqueous ammonia solution; and a second calcination step in which the washed powder precursor is heat-treated at a holding temperature of over 850°C and 950°C to obtain zirconia powder.

[0055] In the first calcination step, a zirconia sol obtained using zirconium chloride is mixed with a stabilizing element source and heat-treated at a holding temperature of 600°C to 850°C to obtain a powder precursor.

[0056] Zirconia sol can be any zirconia sol obtained from zirconium chloride as a raw material. Examples of methods for producing zirconia sol include hydrothermal synthesis and hydrolysis. In hydrothermal synthesis, zirconia sol is obtained by heat-treating a coprecipitation obtained by mixing zirconium chloride with an alkali, etc., in the presence of a solvent at 100 to 200°C. In hydrolysis, zirconia sol is obtained by hydrolyzing zirconium chloride when heated in the presence of a solvent. Thus, examples of zirconia sol can be zirconia sol obtained by hydrothermal synthesis or hydrolysis, and zirconia sol obtained by hydrolysis is preferred. Examples of zirconium chloride include zirconium oxychloride and zirconium chloride, with zirconium oxychloride being preferred.

[0057] From the viewpoint of improving the moldability of the resulting zirconia powder, the average particle size of the zirconia sol is preferably 0.05 μm or more and 0.20 μm or less.

[0058] The zirconia sol obtained by hydrolysis may be washed and dried. Washing can be done by any method that can remove impurities, for example, by washing with water. Drying can be done by any method that removes moisture appropriately, for example, by drying in an air atmosphere at a temperature between 80°C and 120°C. Impurities that can be removed by washing include components that simply adhere to the surface of the zirconia sol and can be easily removed by washing.

[0059] Examples of alkalis used in the production of zirconia sol include one or more selected from the group consisting of ammonia, sodium hydroxide, and potassium hydroxide. In another embodiment, the alkali may be a compound that decomposes to become basic, such as urea.

[0060] Examples of stabilizing element sources to be mixed with zirconia sol include one or more selected from the group consisting of chlorides, fluorides, nitrates, carbonates, sulfates, acetates, oxides, and hydroxides of the stabilizing elements mentioned above. Preferably, one or more selected from the group consisting of chlorides, fluorides, oxides, and hydroxides is used, and more preferably, at least one of chlorides and oxides is used. When the stabilizing elements are scandium and yttrium, examples of stabilizing element sources include scandium chloride and yttrium chloride.

[0061] The zirconia sol and the stabilizing element source should be mixed until they are homogeneous. The mixing method is arbitrary, but one example is to add the stabilizing element source to the zirconia sol solution. The amount of stabilizing element source added to the zirconia sol solution should be such that the amount of stabilizing element in terms of oxide relative to the zirconia in the zirconia sol solution equals the amount of stabilizing element in the target zirconia powder.

[0062] The zirconia sol mixed with the stabilizing element source is preferably dried. The drying method can be any method that can remove the solvent, the water of hydration of the zirconia sol, and the adsorbed water, for example, by processing in an air atmosphere at 120 to 200°C.

[0063] From the viewpoint of ensuring that the BET specific surface area of ​​the resulting zirconia powder is within an appropriate range while solid-solving stabilizing elements into zirconia, the heat treatment in the first calcination step is preferably performed at a holding temperature of 600°C to 850°C. From the viewpoint of ensuring that the zirconia sol is heated more uniformly, the heating rate to the holding temperature is preferably 30°C / hour to 600°C / hour, or 80°C / hour to 120°C / hour. The atmosphere for the heat treatment is preferably an oxidizing atmosphere, and more preferably an atmospheric atmosphere. The holding time (calcination time) at the above-mentioned holding temperature can be appropriately adjusted according to the amount of zirconia sol subjected to the first calcination step and the characteristics of the heat treatment furnace used for calcination, but examples include 30 minutes to 24 hours, 1 hour to 15 hours, or 1 hour to 10 hours.

[0064] In the washing process, the powder precursor obtained in the first calcination process is washed with an aqueous ammonia solution. This removes any remaining chlorine from the powder precursor. - Therefore, it is possible to convert it into NH4Cl, which is easily sublimated, and it is thought that chlorine can be easily removed by calcination in the second calcination step. Examples of chlorine remaining in the powder precursor include chlorine adsorbed on the zirconia sol (chloride ions derived from the zirconia sol source, etc.). Such chlorine is not sufficiently removed by simply washing the zirconia sol or powder precursor with water, but it can be effectively removed by the manufacturing method of this embodiment, and the amount of chlorine in the resulting zirconia powder can be reduced.

[0065] Cl - From the viewpoint of being able to sufficiently convert to NH4Cl, a preferred method for washing the powder precursor with an aqueous ammonia solution is to add the aqueous ammonia solution to the powder precursor, stir, and remove the solids by filtration. The amount of aqueous ammonia solution added to the powder precursor can be 100 ml or more, 150 ml or more, or 200 ml or more per 100 g of powder precursor. The stirring time can be 10 minutes or more, 15 minutes or more, or 20 minutes or more. This process is preferably repeated two or more times, and more preferably three or more times.

[0066] The ammonia aqueous solution preferably has a pH of 9 or higher or 10 or higher, and more preferably 13.5 or lower or 12.5 or lower. The pH of the ammonia aqueous solution used in the washing process is 9 or higher and 13.5 or lower, or 10 or higher and 12.5 or lower. For example, the ammonia aqueous solution may be within ±1.5 of the center value mentioned above.

[0067] In the second calcination process, the washed powder precursor is heat-treated at a holding temperature between 850°C and 950°C to obtain zirconia powder.

[0068] From the viewpoint of removing chlorine from the powder precursor while ensuring that the BET specific surface area of ​​the resulting zirconia powder is within an appropriate range, it is preferable to perform the calcination in the second calcination step at a holding temperature of over 850°C and up to 950°C. From the viewpoint of ensuring that the zirconia sol is heated more uniformly, it is preferable that the heating rate to the holding temperature be 30°C / hour or more, 80°C / hour or more, and also 600°C / hour or less, or 120°C / hour or less, and can be 30°C / hour or more and 600°C / hour or less, or 80°C / hour or more and 120°C / hour or less. The atmosphere for the heat treatment is preferably an oxidizing atmosphere, and more preferably an atmospheric atmosphere. The holding time (calcination time) at the above-mentioned holding temperature can be appropriately adjusted according to the amount of zirconia sol subjected to the calcination step and the characteristics of the heat treatment furnace used for calcination, but can be 30 minutes or more and up to 24 hours, 1 hour or more and up to 15 hours, or 1 hour or more and up to 10 hours.

[0069] From the viewpoint of controlling the average particle size and the BET specific surface area, the zirconia powder obtained as described above may be pulverized. The pulverization method may be either dry pulverization or wet pulverization, with wet pulverization being preferred.

[0070] Wet grinding involves grinding zirconia powder in the presence of a solvent. In other words, it grinds a zirconia powder slurry. To improve grinding efficiency, the mass percentage of zirconia powder in the zirconia powder slurry (hereinafter also referred to as "slurry concentration") is preferably 30% by mass or 40% by mass or more, and also preferably 55% by mass or less, or 50% by mass or less. For example, it may be 30% by mass or more and 55% by mass or less, or 40% by mass or more and 50% by mass or less.

[0071] The solvent can be water, or even pure water.

[0072] The grinding time can be adjusted as appropriate depending on the wet grinding method, but examples include 15 hours or more, 20 hours or more, or 30 hours or less, or 35 hours or less.

[0073] A particularly preferred grinding method is wet grinding using zirconia balls as the grinding medium, preferably zirconia balls with a diameter of 3 mm or less, and more preferably zirconia balls with a diameter of 2 mm or less. Specific examples of wet grinding include grinding using one or more selected from the group consisting of a vibratory mill, a continuous media stirring mill, and a ball mill, with grinding by a vibratory mill being preferred.

[0074] The zirconia powder may be washed before or after grinding. This can reduce the amount of impurities remaining in the zirconia powder.

[0075] The cleaning method can be any method that can remove impurities; for example, cleaning with pure water is one such example.

[0076] One reason why the powder of this embodiment can be obtained by the manufacturing method of this embodiment is as follows. Specifically, in the manufacturing method of this embodiment, zirconium chloride is used as a raw material, and the first calcination step is carried out under the conditions described above, so that the diffusion of substances promoted by heat treatment is appropriately suppressed by the presence of chlorine.Therefore, by using zirconium chloride as a raw material, an appropriate amount of chlorine is present in the zirconia sol, which prevents excessive diffusion of zirconia and stabilizing elements in the first calcination step (which would result in the BET specific surface area of ​​the resulting zirconia powder becoming too small).Furthermore, in the subsequent washing step, the chlorine remaining in the powder precursor obtained in the first calcination step is converted into ammonium chloride, which is easily sublimated, and then the chlorine can be removed in the calcination step of the second calcination step.As a result, the zirconia powder finally obtained has a reduced chlorine content that inhibits the diffusion of zirconia and stabilizing elements, and it is thought that sintering at a lower temperature is possible when manufacturing a sintered body by firing the zirconia powder.

[0077] [Method for manufacturing zirconia sintered bodies] The zirconia powder of this embodiment can be used in a method for manufacturing a sintered body. A known method can be used to manufacture a sintered body using the zirconia powder of this embodiment, and examples include at least one of the following: a method of sintering a molded body containing the zirconia powder of this embodiment, and a method of calcining a molded body containing the zirconia powder of this embodiment and then sintering the resulting calcined body.

[0078] The shape of the molded body is arbitrary. Examples of molded body shapes include at least one selected from the group consisting of cubic, rectangular, polyhedral, columnar, cylindrical, disc-shaped, approximately spherical, and sheet-shaped, or a shape similar to the target zirconia sintered body, such as a dental prosthesis shape, taking into account thermal shrinkage due to sintering. When the molded body is used as the electrolyte material constituting SOFC / EC, the molded body is preferably in the form of a sheet.

[0079] The molded article containing zirconia powder according to this embodiment can be molded by any method. Known methods can be used for molding the zirconia powder, and examples include one or more selected from the group consisting of die press molding, sheet molding, doctor blade method, calender roll method, injection molding, and cold isostatic pressing (CIP). A specific molding method, for example, involves performing CIP treatment on a primary molded article obtained by die press molding of the powder according to this embodiment. The pressure for die press molding is 20 MPa or more or 30 MPa or more, and also 100 MPa or less or 80 MPa or less, preferably 20 MPa to 100 MPa or 30 MPa to 80 MPa. The pressure for CIP treatment is 98 MPa to 392 MPa. As for sheet molding methods, coating methods or gas phase methods can be used. For example, coating methods include the doctor blade method, calender roll method, printing method, etc. For example, gas phase methods include powder jet deposition, aerosol deposition, gas deposition, cold spray, etc. The zirconia powder used for molding may be zirconia powder or a composition containing zirconia powder.

[0080] Calcined bodies are obtained by heat-treating molded bodies. Examples of calcined bodies include structures in which zirconia particles form neckings. Calcined bodies can be shaped into any desired form by processing using CAD / CAM, making it easier to obtain zirconia sintered bodies of any shape.

[0081] The sintering method for the molded or calcined body can be one or more selected from the group consisting of atmospheric pressure sintering, pressure sintering, and vacuum sintering, and more specifically, at least one of atmospheric pressure sintering and pressure sintering can be exemplified, with atmospheric pressure sintering being preferred. In order to reduce the energy required for sintering and to allow uniform material diffusion, sintering is particularly preferably atmospheric pressure sintering in an atmospheric environment. For atmospheric pressure sintering, the holding temperature can be 1100°C or higher, 1150°C or higher, or 1250°C or higher, and also 1600°C or lower, 1500°C or lower, less than 1400°C, 1350°C or lower, or 1300°C or lower. Applicable temperatures include 1100°C to 1600°C, 1100°C to 1500°C, 1100°C to less than 1400°C, 1100°C to 1350°C, 1050°C to 1300°C, 1100°C to 1300°C, 1150°C to 1300°C, or 1250°C to 1300°C. However, in order to obtain a dense zirconia sintered body at a lower sintering temperature than conventional methods, 1050°C to 1300°C is preferred, 1150°C to 1300°C is more preferred, and 1250°C to 1300°C is particularly preferred. The zirconia powder of this embodiment can produce a dense zirconia sintered body at the wide sintering temperature range described above (for example, 1100°C to 1600°C), but is particularly excellent in that it can produce a dense zirconia sintered body even at low sintering temperatures (for example, 1050°C to 1300°C). Furthermore, as conditions for atmospheric pressure sintering, the holding time at the holding temperature described above can be 1 hour to 24 hours, or 2 hours to 20 hours.

[0082] In this embodiment, the zirconia sintered body preferably has a tetragonal or cubic crystal structure as its main phase, rather than a monoclinic crystal structure, and more preferably a cubic crystal structure. This tends to increase the conductivity of the zirconia sintered body. In this embodiment, "having a cubic crystal structure as its main phase" means that the proportion of cubic crystals in the zirconia crystal structure is the largest.

[0083] The zirconia sintered body of this embodiment has a measured density of 5.44 g / cm³. 3 The above are examples, and preferably 5.56 g / cm³. 3 More preferably, 5.67 g / cm³ 3 That concludes the explanation. For example, if the zirconia sintered body of this embodiment is a sintered body obtained by atmospheric pressure sintering (atmospheric pressure sintered body), the measured density is 6.02 g / cm³. 3 Furthermore, 6.01 g / cm³ 3 The following are some of the advantages of this embodiment. As mentioned above, the zirconia sintered body of this embodiment is densified even when obtained at a low sintering temperature. That is, even when obtained at a low sintering temperature, the measured density of the zirconia sintered body of this embodiment is high as described above (i.e., there are few defects inside), so it has excellent air barrier properties and can be suitably used as an electrolyte material for SOFC / EC.

[0084] The zirconia sintered body of this embodiment preferably has conductivity suitable for a solid electrolyte, and in particular conductivity suitable for a low-temperature solid electrolyte operating at temperatures below 800°C. Specifically, the conductivity at 600°C is 5.0 × 10⁻⁶. -3 The requirements include being between S / cm and 1.0 S / cm, and 1.0 × 10 -2 S / cm or more 8.0×10 -1 It is preferable that the S / cm or less value is acceptable.

[0085] [SOFC / EC and its manufacturing method] SOFC / EC obtained using the powder of this embodiment may include one or more selected from the group consisting of electrolyte-supported cells, fuel electrode-supported cells, and metal-supported cells (hereinafter, these are collectively referred to as "supported cells"). Figures 1 to 3 are schematic diagrams showing the electrolyte-supported cell 100a, fuel electrode-supported cell 100b, and metal-supported cell 100c of this embodiment, respectively. As shown in Figure 1, the electrolyte-supported cell 100a of this embodiment comprises an electrolyte 110a, a fuel electrode 120a, and an air electrode 130a, and has a structure in which the strength of the cell is ensured by the electrolyte 110a. As shown in Figure 2, the fuel electrode-supported cell 100b of this embodiment comprises an electrolyte 110b, a fuel electrode 120b, and an air electrode 130b, and has a structure in which the strength of the cell is ensured by the fuel electrode 120b. As shown in Figure 3, the metal-supported cell 100c of this embodiment comprises an electrolyte 110c, a fuel electrode 120c, an air electrode 130c, and a metal support 140, and has a structure in which the strength of the cell is ensured by the metal support 140.

[0086] A method for manufacturing a support cell includes, for example, a step of firing a laminated precursor having a structure in which an electrolyte precursor layer is sandwiched between a fuel electrode precursor layer and an air electrode precursor layer, wherein the electrolyte precursor layer is an electrolyte precursor sheet containing the powder of this embodiment or a fired product thereof. Two specific manufacturing methods are described below.

[0087] The first manufacturing method involves first mixing the powder of this embodiment with a solvent and a binder to prepare a slurry, coating the slurry onto a substrate such as a polymer film, and drying it to obtain an electrolyte precursor sheet containing the powder of this embodiment. Next, a slurry containing the raw materials for the fuel electrode is coated onto one side of the obtained electrolyte precursor sheet to form a fuel electrode precursor layer, and a slurry containing the raw materials for the air electrode is coated onto the other side to form an air electrode precursor layer, thereby obtaining a laminated precursor. By drying and calcining the obtained laminated precursor, a laminate of electrolytes 110a, 110b, 110c, fuel electrodes 120a, 120b, 120c, and air electrodes 130a, 130b, 130c can be obtained as shown in Figures 1 to 3. In the above example, an example of forming the fuel electrode precursor layer and the air electrode precursor layer on the electrolyte precursor sheet is shown, but the fuel electrode precursor may be formed in sheet form and the electrolyte precursor layer and air electrode precursor layer may be formed on the sheet, or the air electrode precursor may be formed in sheet form and the electrolyte precursor layer and fuel electrode precursor layer may be formed on the sheet. Furthermore, when manufacturing the metal-supported cell 100c shown in Figure 3, a fuel electrode precursor layer, an electrolyte precursor layer, and an air electrode precursor layer may be formed on a metal support 140 made of SUS or the like.

[0088] The second manufacturing method involves obtaining an electrolyte precursor sheet containing the powder of this embodiment in the same manner as the first method described above. Next, the electrolyte precursor sheet is calcined to form electrolytes 110a, 110b, and 110c. A slurry containing the raw materials for the fuel electrode is applied to one side of the obtained electrolytes 110a, 110b, and 110c to form a fuel electrode precursor layer, and a slurry containing the raw materials for the air electrode is applied to the other side to form an air electrode precursor layer, thereby obtaining a laminated precursor. By drying and calcining the obtained laminated precursor, a laminate of electrolytes 110a, 110b, and 110c, fuel electrodes 120a, 120b, and 120c, and air electrodes 130a, 130b, and 130c can be obtained as shown in Figures 1 to 3. In the second manufacturing method, instead of forming the fuel electrode precursor layer and the air electrode precursor layer on the electrolyte 110a, 110b, 110c as described above, the electrolyte precursor layer and the air electrode precursor layer may be formed on the fuel electrodes 120a, 120b, 120c obtained by calcining the fuel electrode precursor, or the electrolyte precursor layer and the fuel electrode precursor layer may be formed on the air electrodes 130a, 130b, 130c obtained by calcining the air electrode precursor.

[0089] According to the manufacturing method described above, since the powder of this embodiment, which can be sintered at low temperatures, is used as the material constituting the electrolytes 110a, 110b, and 110c, the firing temperature of the stacked precursor can be lowered, thereby improving the energy efficiency when manufacturing SOFCs / ECs.

[0090] As the materials constituting the fuel electrodes 120a, 120b, and 120c, known materials can be used. For example, a Ni-zirconia cermet material containing 50% to 70% by mass of nickel and 30% to 40% by mass of zirconia can be used.

[0091] Known materials can be used as the materials constituting the air electrodes 130a, 130b, and 130c, for example, (La 1-x Sr x ) y Co 1-z Fe z O 3-σ(Here, x, y, and z satisfy 0 < x ≤ 0.5, 0.8 ≤ y ≤ 1, and 0 ≤ z ≤ 0.5. σ satisfies 0 ≤ σ). Lanthanum strontium cobalt ferrite represented by these can be exemplified.

[0092] Moreover, another layer may be formed between the electrolytes 110a, 110b, 110c, the fuel electrodes 120a, 120b, 120c, and the air electrodes 130a, 130b. For example, a barrier layer for suppressing the reaction between the electrolyte and the air electrode may be provided between the electrolytes 110a, 110b, 110c and the air electrodes 130a, 130b. Examples of the material constituting the barrier layer include Gd-doped ceria (GDC).

[0093] Solvents and binders used for preparing the slurry can be those known in the art. Examples of the solvent include alcohols, aliphatic hydrocarbons, aromatic hydrocarbons, and acetate esters. Examples of the binder include ethylene copolymers, styrene copolymers, (meth)acrylate copolymers, vinyl acetate copolymers, maleic acid copolymers, polyvinyl butyral resins, vinyl acetal resins, vinyl formal resins, vinyl alcohol resins, waxes, and celluloses such as ethyl cellulose.

[0094] The coating method of the slurry can be the coating method described above. Alternatively, instead of the coating method, a method of depositing the powder, the raw material of the fuel electrode, or the raw material of the air electrode of the present embodiment by the vapor phase method described above may be used.

[0095] The firing conditions for the laminated precursor can be the same as those for the zirconia sintered body manufacturing method described above. Specifically, the laminated precursor obtained using the powder of this embodiment can be fired at the wide temperature range described above (for example, 1100°C to 1600°C), but can also be fired at lower temperatures (for example, 1050°C to 1300°C). In particular, setting the firing temperature of the laminated precursor to 1300°C or lower is preferable from the viewpoint of easily suppressing the reaction between the zirconia powder and nickel contained in the fuel electrode, etc. Furthermore, setting the firing temperature of the laminated precursor to 1250°C or higher is preferable from the viewpoint that, if a barrier layer using GDC is provided in the laminated precursor, the GDC also sinters at around 1250°C, allowing for co-sintering of the powder of this embodiment and the barrier layer. When a barrier layer using GDC is provided in the laminated precursor, and co-sintering of the powder of this embodiment and the barrier layer is not performed, the firing temperature of the laminated precursor can be set to a temperature lower than 1250°C, for example, 1150°C ± 50°C. [Examples]

[0096] The present disclosure will be described below with reference to examples. However, the present disclosure is not limited to these examples.

[0097] (Average sol particle size) The average particle size of zirconia sol was measured using a dynamic light scattering particle size distribution analyzer (UPA-UT151, Microtrac-Bell). The median diameter (D50) at which the particle size distribution and integrated particle size distribution curves intersected the 50% horizontal axis was determined as the average sol particle size. As a pretreatment before measurement, the zirconia sol-containing solution was suspended in pure water and dispersed for 3 minutes using an ultrasonic homogenizer.

[0098] (BET specific surface area) The BET specific surface area of ​​the powder was measured using a specific surface area measuring device (device name: Tristar II 3020, manufactured by Shimadzu Corporation) in accordance with JIS R 1626-1996, using the BET multi-point method (5 points) with nitrogen as the adsorption gas, under the following conditions.

[0099] Adsorption medium: N2 Adsorption temperature: -196℃ Pretreatment conditions: Degassing treatment at 250°C for at least 1 hour in an air atmosphere. (Chlorine content) The chlorine content [mass%] of the powder can be determined by referring to a pre-prepared calibration curve based on the fluorescence X-ray intensity obtained by measuring the powder with a fluorescence X-ray analyzer (instrument name: ZSM PrimusII A-126, Rigaku Corporation). The calibration curve was prepared as follows: Several reference substances with different chlorine concentrations were prepared. 0.2 to 0.5 g of each reference substance was mixed with 2 ml of silver standard solution (Ag concentration 1 g / L), 3 ml of nitric acid, and 15 ml of hydrofluoric acid. The mixture was heated at 170°C for 16 hours to dissolve the reference substance, and the solution was allowed to stand in a cool, dark place for 2 hours. As a result, chloride ions from the reference substance reacted with silver ions from the silver standard solution, causing silver chloride to precipitate. The silver chloride was filtered from the solution, and the amount of precipitated silver chloride was calculated by quantifying the silver ions contained in the filtrate with an ICP emission spectrometer (instrument name: Optima 5300 DV, Perkin Elmer). From the calculation result, the chlorine concentration [mass%] of the reference substance was determined. On the other hand, standard samples were pressure-molded into pellet-shaped samples, and these samples were measured using an X-ray fluorescence analyzer to obtain the X-ray fluorescence intensity. The chlorine concentration obtained in this way was plotted on the x-axis and the X-ray fluorescence intensity on the y-axis, and each reference substance was plotted. An approximate straight line was created from each plot so that the correlation coefficient was 0.950 or higher, and this was used as the calibration curve.

[0100] (Monoclinicity) The monoclinic fraction of the powder was determined from the XRD pattern obtained by XRD measurement using an X-ray diffractometer (Ultima IV, Rigaku Corporation) under the following conditions.

[0101] Radiation source: CuKα radiation (λ=0.15418nm) Measurement mode: Continuous scan Scan speed: 4° / min Step width: 0.02° Measurement range: 2θ = 26.0° ~ 33.0° Acceleration voltage / current: 40mA / 40kV Divergence vertical limiting slit: 10mm Divergence / Induction Slit: 1° Light-receiving slit: open Detector: Semiconductor detector (D / teX Ultra) Filter: Ni filter Goniometer radius: 185mm XRD peaks were detected by profile fitting the XRD pattern after smoothing and background removal using a split pseudo-Voigt function. XRD pattern analysis, including smoothing, background processing, and XRD peak detection, was performed using the analysis program included with the X-ray diffractometer (integrated powder X-ray analysis software PDXL Ver.2.2, manufactured by RIGAKU Corporation) under the following conditions.

[0102] Scherrer constant: 1.000 Smoothing method: Smoothing using β-spline, γ-threshold = 1.50 Background removal method: A straight line connecting the endpoints Kα2 ray removal method: intensity ratio=0.497 Peak search method: Peak top method, alpha cut value = 3.00 Profiling fitting method: Split pseudo-Voigt function The XRD peaks corresponding to each crystal plane of zirconia are XRD peaks with peak tops at the following 2θ.

[0103] XRD peak corresponding to the monoclinic (111) plane: 2θ = 31.5 ± 0.5° XRD peak corresponding to the monoclinic (-111) plane: 2θ = 28.0 ± 0.5° XRD peak corresponding to the tetragonal (101) plane: 2θ = 30.0 ± 0.5° XRD peak corresponding to the cubic (111) plane: 2θ = 30.0 ± 0.5° The XRD peaks corresponding to the tetragonal (101) plane and the cubic (111) plane were measured as a single overlapping peak.

[0104] The monoclinic ratio was determined from the following formula.

[0105] f m =[I m (111)+I m (-111)] / [I m (111)+I m (-111)+I t (101)+I c (111)]×100 In the above formula, f m is the monoclinic ratio, I t (101) is the area intensity of the (101) plane of the tetragonal crystal, I c (111) is the area intensity of the (111) plane of the cubic crystal, I m (111) is the area intensity of the (111) plane of the monoclinic crystal, I m (-111) is the area intensity of the (-111) plane of the monoclinic crystal, and I t (101)+I c (111) corresponds to the area intensity of the XRD peak having a peak top at 2θ = 30.0 ± 0.5°. <�

[0106] The area intensity of each XRD peak was determined by using the calculation program "PRO - FIT" and separating each XRD peak by the method described in H. Toraya, J. Appl. Crystallogr., 19, 440 - 447(1986).

[0107] (Average crystallite size) The average crystallite size of the powder was determined from the main XRD peaks where the (101) plane of the tetragonal crystal and the (111) plane of the cubic crystal overlapped, from the following formula.

[0108] D = κλ / βcosθ In the above equation, D is the average crystallite size (Å), κ is the Scherer constant (κ=1), λ is the wavelength of the measured X-ray (λ=0.15418 nm when CuKα is used as the source), β is the full width at half maximum (FWHM) of the main XRD peak (°), and θ is the Bragg angle of the main XRD peak. Note that β is the FWHM value of the main XRD peak obtained by profile fitting the XRD pattern after smoothing and background removal using a divided pseudo-Voigt function. Profile fitting was performed using the analysis program attached to the X-ray diffractometer (integrated powder X-ray analysis software PDXL Ver.2.2, manufactured by RIGAKU).

[0109] (Average particle size) The powder sample was measured using a Microtrac particle size distribution analyzer (MT3000II, Microtrac-Bell) in HRA mode to obtain volume particle size distribution curves and cumulative volume particle size distribution curves. The average particle size was determined using the accompanying analysis software, with the particle size corresponding to 50% of the volume (median diameter). Prior to measurement, the powder sample was suspended in pure water and dispersed for 10 minutes using an ultrasonic homogenizer as a pretreatment.

[0110] (Measured density) Volume of sintered body [cm³] 3 The value [g / cm] can be obtained from the mass [g] of ]. 3 The measured density was determined as follows: The mass was determined by weighing the sintered body. The volume of the sintered body was determined by the Archimedes method in accordance with JIS R 1634. Prior to measurement, the mass of the dried sintered body was measured, and then the sintered body was placed in water and boiled for 1 hour as a pretreatment.

[0111] (Relative density) The ratio of the measured density of the sintered body to the measured density of the reference sample was determined and expressed as the relative density [%]. A sintered body obtained by sintering under excessive conditions was used as the reference sample.

[0112] First, the zirconia powder of each example or comparative example was placed in an alumina container with a lid, and the alumina container was placed in a HIP apparatus equipped with a carbon heating element. Then, a HIP-treated body was obtained by performing HIP treatment in a weakly reducing atmosphere under the following conditions.

[0113] Pressure medium: Argon gas (purity: 99.9%) Heating rate: 10°C / min Holding temperature: 1250℃ Holding pressure: 150 MPa Holding time: 1 hour After holding, the cooling rate to 300°C was set to 30°C / min.

[0114] Next, the obtained HIP-treated body was sintered at atmospheric pressure at 900°C for 2 hours in an air atmosphere to obtain a sintered body, which was used as the reference sample.

[0115] Example 1 A 2 mol / L aqueous solution of zirconium oxychloride was mixed with pure water to obtain an aqueous solution of zirconium oxychloride with a zirconia (ZrO2) equivalent concentration of 0.8 mol / L. The obtained aqueous solution was hydrolyzed at boiling temperature for 200 hours while stirring to obtain a zirconia sol. The obtained zirconia sol had an average sol particle size of 0.1 μm.

[0116] Scandium chloride was added to the zirconia sol and mixed so that the scandia (Sc2O3) equivalent concentration in the zirconia sol was 6 mol%. After drying in an air atmosphere at 160°C, a powder precursor was obtained by heat treatment in an air atmosphere at 800°C for 2 hours. The chlorine content of the obtained powder precursor was 3% by mass.

[0117] To the powder precursor, an aqueous ammonia solution with a pH between 10 and 11 was added at a ratio of 250 ml per 100 g of powder precursor. After stirring for 30 minutes, the solid content was recovered by filtration. This process was repeated four times, and then the product was dried in an air atmosphere at 160°C, followed by heat treatment at an air atmosphere at 900°C for 2 hours to obtain zirconia powder.

[0118] The obtained zirconia powder was washed with a sufficient amount of pure water to form a slurry, which was then ground for 24 hours in a vibratory mill equipped with 2 mm diameter zirconia balls as the grinding medium. After grinding, it was dried in an air atmosphere at 130°C to obtain the zirconia powder of this example.

[0119] The zirconia powder was press-molded with a mold at a pressure of 70 MPa, and then sintered at atmospheric pressure in an air atmosphere at 1150°C for 2 hours to obtain the zirconia sintered body of this example.

[0120] Example 2 Zirconia powder and zirconia sintered bodies were obtained in the same manner as in Example 1, except that the amount of scandium chloride added to the zirconia sol was changed to an amount that resulted in a scandia equivalent concentration of 10 mol% in the zirconia sol.

[0121] Example 3 Zirconia powder and zirconia sintered bodies were obtained in the same manner as in Example 2, except that yttrium chloride in an amount equivalent to 1 mol% of yttria (Y2O3) in the zirconia sol was further added.

[0122] Comparative Example 1 Zirconia powder and zirconia sintered bodies were obtained in the same manner as in Example 1, except that washing with water was performed instead of washing with an aqueous ammonia solution for the powder precursor.

[0123] Comparative Example 2 Zirconia powder and zirconia sintered bodies were obtained in the same manner as in Example 2, except that washing with water was performed instead of washing with an aqueous ammonia solution on the powder precursor.

[0124] Comparative Example 3 Zirconia powder and zirconia sintered bodies were obtained in the same manner as in Example 2, except that the temperature of the second heat treatment was set to 1000°C, and the grinding of the obtained zirconia powder slurry was modified to grind it for 24 hours in a vibratory mill equipped with 10 mm diameter zirconia balls, followed by grinding it for 24 hours in a vibratory mill equipped with 2 mm diameter zirconia balls.

[0125] Comparative Example 4 Zirconia powder and zirconia sintered bodies were obtained in the same manner as in Example 3, except that washing with water was performed instead of washing with an aqueous ammonia solution on the powder precursor.

[0126] The results are shown in Table 1.

[0127] [Table 1] The zirconia powder used in the example was found to have a higher relative density and denser texture in the zirconia sintered body obtained by firing at 1150°C compared to the comparative example, and it was confirmed to have excellent low-temperature sinterability. [Explanation of Symbols]

[0128] 100a Electrolyte-supported cell 100b Fuel electrode supported cell 100c metal-supported cell 110a, 110b, 110c electrolyte 120a, 120b, 120c fuel electrode 130a, 130b, 130c Air electrode 140 Metal support

Claims

1. It contains chlorine and stabilizing elements, The chlorine content is 0.001% by mass or more and 0.300% by mass or less. The difference between the BET specific surface area after heat treatment at 1000°C for 2 hours in an atmospheric environment and the BET specific surface area before the heat treatment is 3.0 m² / g or more and 30.0 m² / g or less. Zirconia powder containing 75% by mass or more of zirconia.

2. The zirconia powder according to claim 1, wherein the stabilizing element comprises at least one selected from scandium, yttrium, ytterbium, cerium, and samarium.

3. The zirconia powder according to claim 2, wherein the stabilizing element comprises scandium and at least one selected from yttrium, ytterbium, cerium, and samarium.

4. The aforementioned stabilizing element includes scandium, The scandium content, when converted to oxides, is between 5.0 mol% and 11.0 mol%. The zirconia powder according to claim 2 or 3.

5. The BET specific surface area before the aforementioned heat treatment was 11.0 m². ２ / g or more 30.0m ２ / g or less, The BET specific surface area after the heat treatment is 3.0 m². ２ / g or more 10.0m ２ It is less than or equal to / g. The zirconia powder according to any one of claims 1 to 3.

6. In addition to the aforementioned stabilizing element, the additive element includes at least one selected from aluminum, silicon, and germanium. The zirconia powder according to any one of claims 1 to 3.

7. A method for producing zirconia powder according to any one of claims 1 to 3, comprising: a first calcination step of mixing a zirconia sol obtained using zirconium chloride with a stabilizing element source and heat-treating it at a holding temperature of 600°C to 850°C to obtain a powder precursor; a washing step of washing the powder precursor with an aqueous ammonia solution; and a second calcination step of heat-treating the washed powder precursor at a holding temperature of over 850°C and 950°C to obtain zirconia powder.

8. A method for producing a zirconia sintered body using the powder described in any one of claims 1 to 3.

9. A method for producing an electrolyte, using the powder described in any one of claims 1 to 3.

10. A method for manufacturing a solid oxide fuel cell, comprising the step of firing a laminated precursor having a structure in which an electrolyte precursor layer is sandwiched between a fuel electrode precursor layer and an air electrode precursor layer, A method for manufacturing a solid oxide fuel cell, wherein the electrolyte precursor layer is an electrolyte precursor sheet containing the powder described in any one of claims 1 to 3 or a calcined product thereof.

11. A method for manufacturing a solid oxide electrolytic cell, comprising the step of firing a laminated precursor having a structure in which an electrolyte precursor layer is sandwiched between a fuel electrode precursor layer and an air electrode precursor layer, A method for producing a solid oxide type electrolytic cell, wherein the electrolyte precursor layer is an electrolyte precursor sheet containing the powder described in any one of claims 1 to 3 or a calcined product thereof.

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